1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a facsimile, a printer, and a multi-function printer configured to form a toner image on a recording medium by utilizing an electro-photographic process and others and having a fixing apparatus configured to fix the toner image on the recording medium, and more specifically to an image forming apparatus having a low toner laid quantity system configured to consume less toner quantity.
2. Description of the Related Art
With the late development of electro-photographic technique and the increase of demands of the market, a method for visualizing image information through an electrostatic latent image is now being utilized in various fields such as a copier and a printer. In particular, technology for reducing toner consumption has become very important with the increasing demands from the aspects of responses to environment and of lowering costs. This technology for reducing the toner consumption is important also from the aspect of cutting energy generated during a process of fixing toner on the recording medium. This technology has come to play an important role also from the demand on energy saving in the office-oriented image forming apparatus using the electro-photography in particular.
Meanwhile, with the development of digitization and colorization, the electro-photographic image forming apparatus has come to be applied also to a part of the printing field. Such image forming apparatus has come to be practically used remarkably in the fields of graphic arts such as photographs and posters and of short-run printing including on-demand printing. In view of entering to the POD (Print On Demand) market, the electro-photographic system has a feature of on-demand quality as a plate-less printing.
However, the electro-photographic prints have numbers of problems yet to seek market value as output products in terms of a color reproducing range, texture, stability of image quality, correspondency to media or the like.
While accommodating to such problems, the technology for cutting toner consumption is increasingly becoming important with the increase of the consciousness for cutting costs as described above and from the aspect of cutting costs per one sheet of output.
Then, concerning a low toner laid quantity system which is a toner consumption reducing technology, the following proposals have been made for example. Japanese Patent Application Laid-open No. 2004-295144 has proposed a configuration of setting an absolute value of charge electric potential of a photoconductor in a lower condition of 350 to 550 V and of using toner having high tinting strength of 0.3 to 0.7 mg/cm2 so that required image density after fixing an image is assured by toner quantity transferred to a recording medium.
Japanese Patent Application Laid-open Nos. 2005-195670 and 2005-195674 propose a configuration of cutting a maximum single-color toner laid quantity to be less than 0.35 mg/cm2.
It is possible to cut toner consumption by increasing a quantity of pigments within toner and by reducing a total toner laid quantity to that extent. However, if the toner laid quantity is cut, such phenomena that toners cannot closely contact with each other and that a sheet having an irregular surface cannot be masked well by the toner in particular because the toner quantity is cut in a single-color solid image.
Cutting the toner laid quantity also poses such problems that when a color (secondary color) is to be formed by superimposing two layers of toners, colorfulness (coloring property) of the secondary color drops and a color reproducing range is narrowed, because areas where the different colors of toners overlap is decreased.